It is still developed and major features were added lately, like full session management (which, AFAIK, is not yet implemented in Systemd).
I'm not saying that Upstart is better than Systemd, just that it provides everything needed by Ubuntu, including for phablet uses.
Perhaps a transition toward Systemd will be done later, but it's just not needed/justified for now.
Also, note that you can "sudo apt-get install systemd" on your Ubuntu box if you want to
He is still one of the main Mir developer?"23:50 <RAOF> Heh. It's our turn to pull a systemd!" remember how that ended up? for him?
If you talk about this IRC chat, I think it went quite good, considering that he was alone against a bunch of (understandably) angry Wayland devs